Machine Buying advice

Hi All,
I've decided after many years of wanting a CNC Machine, that I should buy one.
I would be looking to cut/route PCBs wood, plastics, alloy and hopefully something a little stronger like stainless steel.

This will be a hobby, and I will not be looking to produce anything on a large scale. When I mention hobby, I do not need to look at a service contract as it is assumed that maintenance would be done by myself. The unit will also need to be movable, as in less than 50kg, and be able to sit on top of a table or floor space.

My budget is approx £600. I have a PC which I can use for this, and I will be looking at freeware software for playing around with.

So, if you don't mind taking a bit of time to answer some questions I have, then please help me out here.

1. Many machines are listed as engraving machines, but you often see a demo of cuts being made. Is "engraving" just used as an identifier to a CNC machine?
2. Very little information is given to cutting steel, is this something left for the industrial machines?
3. How do you normally hold down the material which is being cut? I guess it's oversized and held by screws of clamps, am I right?
4. Can anyone recommend a company which makes units for hobby use? I see a couple pop up on eBay, but of course it's difficult to tell how a unit performs in real life.
5. Anything else? What really simple things have I missed?
Cheers

James